Effect of Trace Sc and Zr on the Mechanical Properties and Microstructure of A1 Alloy 2618

An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was prepared by ingot metallurgy (IM) method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and the tensile properties of alloy specimens were measured at 20℃, 200℃, 250℃ and 300℃. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a primary Al_3(Sc,Zr) phase which could refine the grain because it acts as nuclei of heterogeneous crystallization in the melt during solidification. The secondary Al_3(Sc,Zr) particles were full coherent with matrix and had obvious precipitation hardening effect. They also made the S' phase precipitate more homogeneous. So the strength of alloy increases at both ambient and elevated temperatures without a decrease of ductility. The ductile fracture of alloy occurs by microvoid nucleation, growth and coalescence, so the microvoid coalescence is the dominant fracture mechanism.

In-situ SEM Observation of Monotonic and Cyclic Deformed Structure in Ti-2A1-2.5Zr Alloy

The SEM observation in situ of monotonic and cyclic deformed structure in Ti-ZA1-2.5Zr alloy was performed. The regularity of slippage, crack nucleation, propagation and the typical dislocation configuration were also investigated. The twin and twist play an important role in maintaining homogeneous deformation in the final plastic deformation stage.

Multiplex modification with rare earth elements and P for hypereutectic A1-Si alloys

The effect of rare earth （RE） elements on the morphologies and sizes of Si phases in the hypereutectic A1-Si alloys modified with P was investigated. The results show that the addition of La element to the hypereutectic A1-Si alloys can enhance the effect of P element on the modification of the primary Si phases. In the multiplex modification of RE-P, the primary Si phase is refiner and the shape of the eutectic Si is changed from long needle-like to short rod-like. Moreover, the agglomeration rate of the primary Si phase is slowed greatly. Even the melt is held for 6 h, the average size of the primary Si phase is still satisfied. The results analyzed by scanning electron microscope （SEM） indicate that La is richer at A1-Si interface than that in α-A1 or primary Si phase. The higher the La content in the A1-Si interface, the smaller the primary Si phase.

Microstructure characteristics and mechanical properties of steel stud to Al alloy by CMT welding-brazing process

Cold metal transfer （CMT） welding of nickel-coated Q235 steel studs with 606l Al alloy was carried out using ER4043 as filler metal. The welding process was stable, and appearance of weld formed well without surface defect under the parameters of welding current 121 A, welding voltage 15.4 V and welding speed 6 r/min. The microstructure of fiUer metal was analyzed by means of scanning electron microscopy. The filler metal and 6061 Al alloy were fused to form fusion welding interface, the fusion zone had a good bonding without any micro defect. The steel stud did not melt and brazing interface was formed between the filler metal and steel stud. Two different reaction layers existed in the brazing interface, the Fe2Al5 layer about 10 -12 p^m formed near the steel stud side, and the other layer was mainly composed of FeAl3. Nickel-rich zone was formed in the root toe area of the fillet weld, which was mainly composed of Al3Ni2. The tensile tests showed that the maximum shearing strength of the joints was 129 MPa. The joint was brittle fractured in the intermetallic compound layer where plenty of FeAl3 were distributed continuously.

INFLUENCE OF AGING ON MICROSTRUCTURE AND TENSILE BEHAVIOR OF AI ALLOY 8090

The variations of microstructure and tensile behavior of an Al-Li-Cu-Mg-Zr alloy during aging are studied in this paper. It has been found that the fine δ-phase precipitated in the underaging condition and that the δ-, S-and T1-phases precipitate in the peak aging and the overaging conditions. The alloy exhibits transgranular fracture on the underaging condition, and mixture of transgranular and intergranular ruptures in the peak aging and overaging conditions.

STUDY ON THE HOT DEFORMATION BEHAVIORS OF Al-Zn-Mg-Cu-Cr ALUMINUM ALLOY

The hot deformation behaviors and microstructures of A1-Zn-Mg-Cu-Cr aluminum alloy have been studied using thermal simulation test, optical microscopy and transmission electron microscopy. As a result, the true stress versus true strain curves and the microstructures under various deformation conditions are obtained. The microstructures gradually incline to dynamic-recrystallization with the deformation temperature rising and the recrystallization grains refine with the decrease of deformation temperature or with raising the strain rates. The quantitative relationship between the Zener-Hollomon parameter （Z） and average recrystallization grain size in the subsequent heat treatment is set up.

Characterization of mechanical properties of aluminum cast alloy at elevated temperature

The tensile response, the low cycle fatigue （LCF） resistance, and the creep behavior of an aluminum （A1） cast alloy are studied at ambient and elevated temperatures. A non-contact real-time optical extensometer based on the digital image correlation （DIC） is developed to achieve strain measurements without damage to the specimen. The optical extensometer is validated and used to monitor dynamic strains during the mechanical experiments. Results show that Young＇s modulus of the cast alloy decreases with the increasing temperature, and the percentage elongation to fracture at 100 ℃ is the lowest over the temperature range evaluated from 25 ℃ to 300 ℃. In the LCF test, the fatigue strength coefficient decreases, whereas the fatigue strength exponent increases with the rising temperature. The fatigue ductility at 100 ℃. As expected, the resistance to and changes from 200 ℃ to 300 ℃. coefficient and exponent reach maximum values creep decreases with the increasing temperature

Grain refining of Er added to Ti-22Al-25Nb alloy and morphology of erbium precipitates

In order to investigate the effect of erbium （Er） on the microstructure of orthorhombic Ti2A1Nb-based alloys, four testing alloys were prepared by adding differ- ent contents of the rare earth metal Er to Ti-22A1-25Nb alloy and optical microscopy, X-ray diffraction, scanning electron microscopy, electron probe microanalysis, energy- dispersive spectrometry, and transmission electron microscopy were used. The results show that the addition of Er is capable of grain refining and the refinement effect is more obvious with increasing content of Er. The Er203 dispersoids formed by internal oxidation and A13Er com- pound particles are observed in Er-doped alloys and the number of Er precipitates is increased with increasing Er addition. It is likely that the solubility of Er in the Ti2A1Nb alloy is very low and Er precipitates tend to segregate at grain boundaries, which together with the surface activity of rare earth elements is supposed to decrease the prior B2 grain size of Ti-22A1-25Nb alloy effectively.

The Enhanced Effect of Optical Emission from Laser Induced Breakdown Spectroscopy of an Al-Li Alloy in the Presence of Magnetic Field Confinement

In this paper, the influence of magnetic field strength on laser-induced breakdown spectroscopy （LIBS） has been investigated for various pressures. The plasma plume was produced by employing Q-switch Nd：YAG laser ablation of an A1-Li alloy operating at a 1064 nm wavelength. The results indicated that the LIBS intensity of the A1 and Li emission lines is boosted with an increase of magnetic strength. Typically, the intensity of the A11 and Li I spectral emissions can be magnified by 1.5-3 times in a steady magnetic field of 1.1 T compared with the field-free case. Also, in this investigation we recorded time-resolved images of the laser-produced plume by employing a fast ICCD camera. The results show that the luminance of the plasma is enhanced and the time of persistence is increased significantly, and the plasma plume splits into two lobes in the presence of a magnetic field. The probable reason for the enhancement is the magnetic confinement effect which increases the number density of excited atoms and the population of species in a high energy state. In addition, the electron temperature and density are also augmented by the magnetic field compared to the field-free case.

Effect of AlP master alloy on grain refinement of primary silicon in eutectic Al-Si alloys

To obtain the finer primary silicon crystals, the proprietary Al-P masteralloy was adopted to modify the eutectic Al-Si alloys and the most suitable modification process wasmade in the experiments. The SEM (Scanning Electron Microscope) and DSC (Differential ScanningCalorimeter) analysis indicate that the Al-P modifier has more advantages over Cu-P and Fe-Pmodifier in easily addition, no elemental alteration and less undercooling of primary silicon'ssolidification, which suggests the Al-P master alloy is an effective modifier of eutectic Al-Sialloys.

MICROSTRUCTURE-PROPERTY RELATIONSHIP OF Al-2.2Li-2.5Cu-0.2Mg ALLOY

The relationship among the microstructures,properties and the phase transformation in Al-2.2Li-2.5Cu-0.2Mg alloy after various treatments have been studied by optical microscopy and TEM observations.It is verified that solution treated at 525℃ for 1h is saris- factory for this alloy in which all the alloying elements are dissolved in the α-Al matrix,and aging at 190℃ for 16 h is the peak-aged condition.The alloy subjected to treatment is strengthened only be T_1 phase.In overaged or underaged conditions,the alloy is strengthened by two phases,in this cases,the strengthening effect is smaller than that by one phase.The deformation prior to aging would develop the plasticity and do not decrease the strength of the experimental alloy.

EFFECT OF Cu ON MICROSTRUCTURE AND PROPERTIES OF Al-Li ALLOYS

The aging precipitation structure and the properties of Al-Li-Cu-Zr alloys with 3 different Cu/Li ratios have been studied.Experimental results show that the aging hardening of the alloys consists of two steps:The first is strengthened by δ′-phase(δ′+T_1 phase in alloy No.3),and the second by δ′+T_1 phase(δ′+T_1+θ′phase in alloy No.3).The plate of T_1-phase can absorb the Li atoms from δ′ particles when the plate bumped into δ′-phase,and therefore, these δ′ phase particles become smaller and gradually disappear.The strength and hardness increase with the increase of Cu/Li ratio and cuases a decrease in plasticity.The crack mode would change from transgranular to intergranular.This is due to the precipitation of the equi- librium phases contained Cu at grain boundaries.

Superplastic Forming and Diffusion Bonding for Sandwich Structure of Ti-6Al-4V Alloy

Superplastic forming and diffusion bonding (SPF/DB) is a well-established process for the manufacture of components almost exclusively from Ti-6AI-4V sheet material. The sandwich structure of Ti-6AI-4V alloy is investigated. The effects of the microstructure on the SPF/DB process were discussed. The microstructure at the interfaces and the distribution of thickness were researched.

Microstructure and Properties of 7075Al Alloy Fabricated by Directly Combined of Spray Forming and Continuous Extrusion Forming under Different Atomization Gas Pressures

A new process consisting of the spray forming and the continuous extrusion forming for manufacturing 7075A1 alloy was proposed. The microstructure evolution, mechanical properties and the resistance to stress corrosion cracking of the alloy were studied. The results indicate that the spray forming process induces obviously grain refinement and greatly lower segregation microstructure. Besides, the Conform process produces finer grains and conduces to more uniform distribution of the precipitates of A1Cu and MgZn2 phases. The fabricated alloy shows good comprehensive mechanical properties and superb performance of stress corrosion resistance. Moreover, a better combination of the mechanical properties and the resistance to stress corrosion cracking could then be obtained under a certain condition of atomization gas pressure of 0.19 MPa. The enhanced properties are attributed to the following factors, which include the grain refinement, the fine and homogeneous distribution of A1Cu and MgZn2 phases, the high density of the extruded products, as well as the discontinuous distribution of the grain boundaries after retrogression and reaging （RRA） heat treatment.

Homogenization heat treatment of 2099 Al–Li alloy

Abstract The microstructure evolution and composition distribution of as-cast and homogenized 2099 aluminumlithium （Al-Li） alloy were studied by optical microscopy （OM）, differential thermal analysis （DTA）, scanning electron microscopy （SEM）, energy dispersive spectrometry （EDS）, area and line scanning, X-ray diffraction （XRD）, and Vickers microhardness test methods. The results show that severe dendrite exists in the as-cast alloy. Cu, Zn, Mn, and Mg distribute unevenly from the grain boundary to inside. The low-melting point nonequilibrium eutectic phases dis- solve into the matrix during the first-step homogenization, whereas the melting point of residual eutectic phases is elevated. After the second-step homogenization, most of the remaining eutectic phases dissolve into the matrix, except a small amount of A1-Cu-Fe phases. An optimized homogenization process of the 2099 A1-Li alloy is developed （515℃ - 18 h ＋ 525℃ - 16 h）, which shows a good agreement with the homogenization kinetic analysis results.

On the modification of hypereutectic Al-Si alloys using rare earth Er

Hypereutectic Al-17.5Si （wt pct） and Al-25Si （wt pct） alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.

Composition and corrosion resistance of cerium conversion films on 2195Al-Li alloy

The Ce conversion films on 2195A1-Li alloy without and with post-treatment were studied and the corrosion resistance was evaluated as well. The surface morphology was observed by scanning electron microscopy （SEM）, and the chemical composition was characterized by X-ray photoelectron spectroscopy （XPS）. The corrosion behaviors of 2195A1-Li alloy and conversion coating were assessed by means of potentiodynamic polarization curves. The experimental results indicated that after post-treatment the surface quality was improved significantly. According to XPS, the conversion coating after post-treatment was mainly composed of CeO2, Ce203, Ce-OH and a little MoO3 and MOO2. The results of potentiodynamic polarization curves revealed that the conversion coating with post-treatment possessed better corrosion resistance than bare alloy and Ce conversion coating without post-treatment.

Inverse identification of constitutive parameters of Ti_2AlNb intermetallic alloys based on cooperative particle swarm optimization

Ti_2AlNb intermetallic alloy is a relatively newly developed high-temperature-resistant structural material, which is expected to replace nickel-based super alloys for thermally and mechanically stressed components in aeronautic and automotive engines due to its excellent mechanical properties and high strength retention at elevated temperature. The aim of this work is to present a fast and reliable methodology of inverse identification of constitutive model parameters directly from cutting experiments. FE-machining simulations implemented with a modified Johnson-Cook（TANH） constitutive model are performed to establish the robust link between observables and constitutive parameters. A series of orthogonal cutting experiments with varied cutting parameters is carried out to allow an exact comparison to the 2 D FE-simulations. A cooperative particle swarm optimization algorithm is developed and implemented into the Matlab programs to identify the enormous constitutive parameters. Results show that the simulation observables（i.e., cutting forces, chip morphologies, cutting temperature） implemented with the identified optimal material constants have high consistency with those obtained from experiments,which illustrates that the FE-machining models using the identified parameters obtained from the proposed methodology could be predicted in a close agreement to the experiments. Considering the wide range of the applied unknown parameters number, the proposed inverse methodology of identifying constitutive equations shows excellent prospect, and it can be used for other newly developed metal materials.

Fatigue crack initiation for Al-Zn-Mg alloy welded joint

To investigate fatigue crack initiation characteristics of A1-Zn-Mg alloy welded joint, notched specimens were used in fatigue test for the base metal, welding bead and heat affected zone （HAZ）. The fatigue fracture surface near the fatigue crack initiation site was observed by scanning electron microscope （SEM）. The results show that the differences of fatigue crack initiation life among base metal, welding bead and HAZ are not obvious. Inhomogeneity in microstructure and mechanical performance of HAZ influences the fatigue crack initiation life. The ratio of fatigue crack initiation life （Ni） to fatigue failure life （Nf） for the base metal, welding bead and HAZ of A7N01 aluminium alloy welded joint are 26.32%, 40.21% and 60.67%, respectively. Fatigue crack initiation life can be predicted using a uniform model. Observation of fatigue fracture surfaces shows that for the welding bead a fatigue crack initiates from the smooth surface due to the welding process, the blowhole in HAZ causes fatigue crack and the crushed second phase particles play an important role in fatigue crack initiation for the base metal.

Electrochemical Formation of AI-Li Alloys by Codeposition of AI and Li from LiCI-KCI-AIF3 Melts at 853 K

The electrochemical behavior of AI（III） ions was studied in molten LiC1-KC1 melts on a molybdenum electrode. Cyclic voltammetry, chronopotentiometry and chronoamperometry were used to explore the deposition mechanism of A1 and Li. Cyclic voltammetry expriment indicates that under potential deposition（UPD） of lithium on pre-deposited aluminium led to the formation of liquid A1-Li alloys at 853 K. The diffusion coefficient of AI（III） ions at 853 K in LiC1-KC1-AIF3（I%, mass fraction） melts was determined to be （2.79~0.05）x 10_5 cm2/s. Chronopotentio- grams and chronoamperograms demonstrate that the codeposition of AI（III） and Li（I） ions formed A1-Li alloys at ca- thodic current densities higher than -0.28 A/cm2 or cathodic potentials more negative than -2.20 V. X-Ray diffrac- tion（XRD） pattern indicates that A1-Li alloys with different phases formed via galvanostatic electrolysis. Inductively coupled plasma（ICP） analyses of the samples obtained by electrolysis show that lithium and aluminium contents of A1-Li alloys could be controlled by A1F3 concentration and current intensity.